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Introduction Longitudinal imaging of transgenic mice and mouse disease models allows studies to be performed over their entire life span. Narrow-vertical bore magnets (microimagers) are well suited for imaging mice –low cost –availability at high fields –availability of high-performance gradients While anatomical imaging is readily available, fMRI in mice on microimagers remains a major challenge

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Introduction Other challenges include –Limited spaces for physiological monitoring –More difficult to use mechanical ventilation –Increased susceptibility-induced signal loss due to small brain size and larger air-tissue interfaces The goal of this study was –To develop a sensory-stimulation mouse model for fMRI studies –Explore echo-planar imaging for fMRI on a 9.4 T microimager

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Methods Three sets of experiments were performed: –Graded isoflurane (0.25, 0.50, 0.75, 1.0, 1.25%) were explored using 10% CO 2 to determine the optimal BOLD CNR (n = 9) –Hindpaw electrical stimulation (1-7 mA) on mice anesthetized under the optimal isoflurane level (n = 6) –Stimulation were explored in details with 4 and 6 mA and under 0.75% and 1.0% isoflurane (n = 5) Relatively high currents were used because isoflurane is a potent anesthetic, relative to the widely used -chloralose Bench top observations were also observed in some of the hindpaw-stimulation animal and four additional animals

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Data analysis Hypercapnia –BOLD percent changes were calculated from a whole-brain ROI –BOLD contrast-to-noise ratio (CNR) was computed Hindpaw stimulation –Cross-correlation maps were calculated –ROIs of the hindpaw primary sensory cortex was drawn with reference to the average of all activation maps and anatomy –Time courses of different conditions were obtained from the same ROIs without using an activation-map mask –Percent changes were computed

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Conclusions Implemented spin-echo EPI for fMRI study Developed a mouse model for sensory stimulation fMRI study –Optimized isoflurane concentration –Stimulation currents These optimal parameters are in good agreement with an isoflurane- anesthetized sensory-stimulation model in rats where MABP, HR and RR and blood-gas measurements were carefully monitored. Improvement in spatial resolution and BOLD contrast are under investigation.